1(a) This question is about the chemistry of compounds containing phosphorus.
Phosphorus forms several acids including H3PO4 and H3PO3.
H3PO4 is a tribasic acid. The equilibria for the dissociations are shown below.
1 H3PO4 ⇌ H+ + H2PO4–
2 H2PO4– ⇌ H+ + HPO42–
3 HPO42– ⇌ H+ + PO43–
i. During the equilibria, H2PO4– behaves both as an acid and as a base.
Explain this statement, using the equilibria 1, 2 and 3, as required.
[2]
ii. In a H3PO3 molecule, the O atoms are covalently bonded to the P atom. The H atoms are bonded to the O
atoms.
Draw the structure of a H3PO3 molecule, showing all the bonds.
On your diagram, add the values for the O–P–O and P–O–H bond angles.
[3]
iii. The systematic name of H3PO4 is phosphoric(V) acid.
What is the systematic name of H3PO3?
[1]
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, (b) Phosphine, PH3, is a poisonous gas.
i. Phosphine reacts with oxygen gas to form phosphorus(V) oxide and water.
Write the equation for this reaction.
[1]
ii. Aqueous silver nitrate, AgNO3, is reduced by PH3.
The unbalanced equation is shown below.
Balance the equation and use oxidation numbers to explain why this is a redox reaction.
........ AgNO3 + ........ PH3 + ........ H2O ........ Ag + ........ H3PO3 +........ HNO3
Explanation
[3]
2 This question is about iron.
Iron can be extracted from iron ores containing the oxide Fe2O3.
i. What is the systematic name for Fe2O3?
[1]
ii. Balance the equation for the reduction of Fe2O3 with carbon monoxide.
......... Fe2O3 + ......... CO → ......... Fe + ......... CO2
[1]
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, 3 Which reaction does not show disproportionation of chlorine?
A MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O
B Cl2 + H2O → HCl + HClO
C 2ClO2 + 2NaOH → NaClO2 + NaClO3 + H2O
D 2NaOH + Cl2 → NaCl + NaClO + H2O
Your answer [1]
4 Which equation does not represent a disproportionation reaction?
A Cl2 + H2O → HClO + HCl
B Cl2 + 2NaOH → NaClO + NaCl + H2O
C 4KClO3 → KCl + 3KClO4
D 4HCl + MnO2 → MnCl2 + Cl2 + 2H2O
Your answer [1]
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, 5(a) This question is about energy changes.
Hydrogen peroxide decomposes as shown in Reaction 16.1.
Reaction 16.1
The table shows enthalpy changes of formation and entropies.
ΔHfe/kJ mol1 Se / J K–-1 mol–1
H2O2(l) –188 110
H2O(l) –286 70.0
O2(g) 0 205
i. Calculate the free-energy change, ΔG, in kJ mol–1, of Reaction 16.1 at 25 °C.
Give your answer to 3 significant figures.
ΔG = .............................................. kJ mol–1 [4]
ii. The decomposition of hydrogen peroxide shown in Reaction 16.1 is feasible.
Suggest why Reaction 16.1 does not take place at 25 °C despite being feasible.
[1]
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Phosphorus forms several acids including H3PO4 and H3PO3.
H3PO4 is a tribasic acid. The equilibria for the dissociations are shown below.
1 H3PO4 ⇌ H+ + H2PO4–
2 H2PO4– ⇌ H+ + HPO42–
3 HPO42– ⇌ H+ + PO43–
i. During the equilibria, H2PO4– behaves both as an acid and as a base.
Explain this statement, using the equilibria 1, 2 and 3, as required.
[2]
ii. In a H3PO3 molecule, the O atoms are covalently bonded to the P atom. The H atoms are bonded to the O
atoms.
Draw the structure of a H3PO3 molecule, showing all the bonds.
On your diagram, add the values for the O–P–O and P–O–H bond angles.
[3]
iii. The systematic name of H3PO4 is phosphoric(V) acid.
What is the systematic name of H3PO3?
[1]
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, (b) Phosphine, PH3, is a poisonous gas.
i. Phosphine reacts with oxygen gas to form phosphorus(V) oxide and water.
Write the equation for this reaction.
[1]
ii. Aqueous silver nitrate, AgNO3, is reduced by PH3.
The unbalanced equation is shown below.
Balance the equation and use oxidation numbers to explain why this is a redox reaction.
........ AgNO3 + ........ PH3 + ........ H2O ........ Ag + ........ H3PO3 +........ HNO3
Explanation
[3]
2 This question is about iron.
Iron can be extracted from iron ores containing the oxide Fe2O3.
i. What is the systematic name for Fe2O3?
[1]
ii. Balance the equation for the reduction of Fe2O3 with carbon monoxide.
......... Fe2O3 + ......... CO → ......... Fe + ......... CO2
[1]
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, 3 Which reaction does not show disproportionation of chlorine?
A MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O
B Cl2 + H2O → HCl + HClO
C 2ClO2 + 2NaOH → NaClO2 + NaClO3 + H2O
D 2NaOH + Cl2 → NaCl + NaClO + H2O
Your answer [1]
4 Which equation does not represent a disproportionation reaction?
A Cl2 + H2O → HClO + HCl
B Cl2 + 2NaOH → NaClO + NaCl + H2O
C 4KClO3 → KCl + 3KClO4
D 4HCl + MnO2 → MnCl2 + Cl2 + 2H2O
Your answer [1]
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, 5(a) This question is about energy changes.
Hydrogen peroxide decomposes as shown in Reaction 16.1.
Reaction 16.1
The table shows enthalpy changes of formation and entropies.
ΔHfe/kJ mol1 Se / J K–-1 mol–1
H2O2(l) –188 110
H2O(l) –286 70.0
O2(g) 0 205
i. Calculate the free-energy change, ΔG, in kJ mol–1, of Reaction 16.1 at 25 °C.
Give your answer to 3 significant figures.
ΔG = .............................................. kJ mol–1 [4]
ii. The decomposition of hydrogen peroxide shown in Reaction 16.1 is feasible.
Suggest why Reaction 16.1 does not take place at 25 °C despite being feasible.
[1]
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